The present invention relates to a method and an apparatus for the detection of foreign materials in moving textile materials, in particular to the detection of foreign fibres or foreign materials in moving yarns, threads, slivers, and unformed fibre bands, cords, ropes, including monofilament and multifilament threads. The present invention may find advantageous use in all sorts of textile machinery, including, but not limited to, weaving or knitting or spinning machines, in particular, ring-, open-end-, air-jet- or chemical spinning machines, bobbin winding machines, carding machines, drawing benches, combing machines, bobbin frames or texturing machines.
Various methods of detecting foreign fibres in moving textile materials have been described, for example, those based on optical methods. WO 98/33061 and EP-A-652 432 are examples of such methods. These methods are excellent but generally require the selection of frequencies of light which are able to distinguish foreign materials from the virgin thread material. Sometimes this is difficult if the colour and/or light absorbency of both the foreign and the virgin fibre are very similar.
Triboelectric detection heads have been used for determining the presence of the movement of threads or fibres as disclosed in U.S. Pat. No. 3,676,769 or U.S. Pat. No. 4,027,232. These include a probe which picks up electrical signals from the moving thread or yarn. The electrical signal generated by relative movement between a textile thread and an object is best described as a form of noise. This undifferentiated signal has found use in deciding if a yarn or thread is broken, i.e. if relative movement has stopped.
It is known that different materials provide different triboelectric voltages and/or currents. U.S. Pat. No. 5,341,103 describes a method of measuring the triboelectric charge on a moving flexible strip of material of short length. U.S. Pat. No. 4,885,543 describes a method of measuring triboelectric voltages on bulk materials. As explained in this latter document the results of triboelectric testing of different materials is often unreliable due to the great variations in values. A further aspect which is clearly demonstrated from the test results in this document is that many materials hold their triboelectric charge for a considerable length of time, e.g. 120 seconds or more. This is well known in processing industries where the charging up of moving sheets is a major cause of concern. It also means that any measurement of triboelectricity depends upon the previous history of the material being tested. This can be a source of unreliability and variability in the measurements.
It is an object of the present invention to provide a method and an apparatus for the detection of foreign materials in moving textile materials which allows detection even when the foreign material is optically almost identical to that of the virgin fibre.
In particular, it is an object of the present invention to provide a method and an apparatus for the detection of foreign materials in moving textile materials which can be used in existing textile machines without requiring a redesign of such equipment.
The present invention includes the use of a triboelectric probe to detect foreign materials in a moving textile material, in particular in moving threads, yarns or slivers.
The present invention may provide a method for detecting foreign materials in a moving textile material, in particular in moving threads, yarns or slivers, comprising the steps of:
generating relative motion between the textile material and a probe;
measuring electric signals picked up by the probe from the textile material;
comparing the measured electric signals with a value representative of the textile material without foreign material; and
determining from the comparison whether foreign material is present in the textile material.
The present invention may include an apparatus for detecting foreign materials in a moving textile material, in particular in moving threads, yarns or slivers, comprising: a probe for picking up electric signals from the textile material; a comparator for comparing the output of the probe with a reference value and being adapted to provide a signal representative of detection of a foreign material in the textile material.
The dependent claims define further individual embodiments of the present invention.